It is common practice to detect the moisture level of clothes tumbling in a dryer by the use of sensors located in the dryer drum. A voltage signal from the moisture sensor is used to estimate the moisture content of the articles being dried based on the actual characteristics of the load being dried. The sensors are periodically sampled to provide raw voltage values that are then filtered or smoothed, and inputted to a processor module that determines when the clothes are dry, near dry, or at a target level of moisture content, and the drying cycle should terminate.
The filtered voltage is typically compared with a target voltage stored in memory associated with the microprocessor. This target voltage is a predetermined voltage determined for the dryer. Once the target voltage is reached, this is an indication to the dryer that a predetermined degree of dryness for the load has been reached. The microprocessor controls the drying cycle and/or cool down cycle of the dryer in accordance with preset user conditions and the degree of dryness of the load in the dryer relative to the target voltage.
The target voltage is chosen for a predetermined or average load size and a preset air flow rate for the dryer. This target voltage may not accurately reflect different load sizes and differing air flow conditions for the dryer resulting in the automatic drying cycle either drying the clothing too long or insufficiently.
For example, the smaller the load the higher the target voltage should be set because larger loads are in contact with the sensors more frequently and this reduces the value of the filtered voltage signal.
Also, the air flow influences the level of the smoothed or filtered voltage signal. The greater the air flow through the dryer the more clothes are pulled towards the front of the dryer increasing the frequency of contact of the clothing with the moisture sensor when the moisture sensor is mounted at the front of the dryer drum.
Accordingly, there is a need for a drying algorithm that sets its target voltage associated with the moisture content of the clothes and which takes into consideration the influences associated with load size and/or air flow condition.